Surface preparation and polymeric coating of continuous-strip flat-rolled steel and coated product

ABSTRACT

Engineered composite coated flat-rolled steel strip is produced in continuous line operations, in which flat-rolled steel strip, free of surface iron oxide, having a metallic corrosion-protective coating, is polymer coated in continuous-line operations in which a plurality of adherent thin-film layers of polymeric material are deposited on a strip surface. In a dual-surface polymeric coating embodiment, each surface is separately-pretreated for surface adhesion, solidified, and polymeric overhang is removed. Finish processing re-melts the polymer coating and rapidly cools that coating through glass-transition temperature to establish amorphous characteristics in the polymeric coating materials. An anhydride-modified polypropylene, first contacts the strip, an intermediate layer can include about fifteen to twenty five percent, by weight, polybutylene with the balance polypropylene; an outer surface polymeric layer includes about five to ten percent, by weight, polybutylene with the balance polypropylene.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/357,218 filed Feb. 15, 2002; and, is acontinuation-in-part of co-owned and co-pending U.S. patent applicationSer. No. 10/156,471 entitled “METHODS AND APPARATUS FOR SURFACEPREPARATION AND DUAL POLYMERIC LAYER COATING OF CONTINUOUS-STRIPFLAT-ROLLED SHEET METAL, AND COATED PRODUCT” filed May 15, 2002 as acontinuation-in-part of co-owned U.S. patent application Ser. No.09/490,305 filed Jan. 24, 2000, entitled “Polymeric Coated Metal Stripand Method for Processing Same”.

INTRODUCTION

This invention relates to composite-coating of continuous-stripflat-rolled steel including activating a single substrate surfaceat-a-time to enhance polymeric adhesion and facilitate continuous-linepolymeric coating operations. More particularly, this invention isconcerned with simultaneous extrusion deposition of selected multiplepolymeric materials and providing for uniform thickness polymericcoating of engineered composite-coated work-product.

OBJECTS OF THE INVENTION

An important object involves selecting multiple thermoplastic polymersfor providing surface toughness while maintaining surface flexibility ofpolymeric-coated rigid flat-rolled steel.

A related object combines composite-coating of rigid flat-rolled steelsubstrate for increasing fabricating capabilities for, and durabilityof, market-usage fabricated product.

A more specific object provides for extrusion of multiple moltenpolymeric coating materials for coating: continuous-strip steel, free ofstrip heating requirements, while traveling in a continuous-line.

A further object provides surface activation of metalliccorrosion-protected continuous-strip steel substrate for bondingpolymeric coating materials during continuous-line manufacture ofengineered composite-coated work-product.

Other objects, advantages, and contributions are set forth in disclosingembodiments of the invention shown in the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagrammatic flow chart for describing processing of theinvention for selective single surface and dual-surface polymericcoating embodiments of continuous-line operations;

FIG. 2 is an enlarged schematic cross-sectional view of surfacepre-treatment apparatus for describing surface-activating methods andapparatus of the invention for enhancing polymeric adhesion;

FIG. 3 is a schematic perspective view, partially in cross-section, fordescribing supply and preparation of selected thermoplastic polymericcoating materials for extrusion in accordance with the invention;

FIG. 3A is an enlarged schematic cross-sectional view, of a designatedportion of FIG. 3, for describing principles of the invention for meltedextrusion deposition of multiple polymeric materials during in-linetravel of continuous-strip;

FIG. 4 is a schematic perspective view, partially in cross-section, fordescribing continuous-line apparatus for surface activation and meltedpolymer extrusion in a single-surface polymeric-coating embodiment ofthe invention, including finish-processing of that surface;

FIG. 5 is an enlarged cross-sectional view for describing metalliccorrosion production of flat-rolled steel in accordance with theinvention and single-surface polymeric coating, as produced by utilizingthe continuous-line embodiment of FIG. 4;

FIG. 6 is a schematic view, partially in cross-section, of dual-surfacepolymeric-coating continuous-line apparatus of the invention, fordescribing separately pre-treating and polymeric coating a singlesurface at-a-time of rigid flat-rolled steel substrate continuous-strip,including simultaneous finish-processing of both surfaces;

FIG. 7 is an enlarged cross-sectional view of engineeredcomposite-coated work-product of the invention for describing metallicsub-surface protection and dual-surface polymeric coating produced byutilizing the embodiment of FIG. 6;

FIG. 8 is a schematic-perspective view for describing types andadvantages of polymeric-coated building-construction structures asfabricated from engineered composite-coated work-product of theinvention, and

FIG. 9 is an enlarged cross-sectional view of a designated portion ofFIG. 8 for describing composite-coating selections of the invention forincreasing durability of market-usage product.

DETAILED DESCRIPTION

Referring to FIG. 1, supply of continuous-strip corrosion-protectedflat-rolled steel is controlled at station 20 for surface pre-treatmentsteps. A single surface is pre-treated at-a-time for activation of thatsurface for enhancing adhesion of a selected thermoplastic polymericmaterial of the invention. Surface pre-treatment flame impingement iscarried out at station 22; ionization of gas contiguous to that surface,preferably by corona-discharge, can be carried out at station 24 of FIG.1; and, pre-treatment flame-impingement and surface-gas ionization stepscan be combined.

Flame impingement is a preferred initial pre-treatment step.Coiling-lube solution as used by some flat-rolled steel mills isburned-off, along with associated debris, by an initial flameimpingement. One or more rows of burners, of the type shownschematically in cross-section FIG. 2, are utilized on the surface beingprepared dependent on line speed; and, those burner rows extend acrossfull surface width of the strip. It is estimated that restricting oxygencontent of the impinging flame produces a surface-reaction causing lossof surface electrons; enabling valence bonding, which could help toexplain the resulting strong adhesion achieved between an organiccoating and an inorganic metallic surface.

Preferably, that single substrate surface is also pre-treated to furtheractivate, or maintain activation of that surface during strip travel, byionizing gas contiguous to that surface, for example, by utilizing oneor more corona discharge electrodes, shown schematically in FIG. 2,which extend in functional relationship across strip width. Acombination of those pre-treatments is preferred so as to establish asurface for aggressively bonding with an anhydride-modified polymericcoating material, which, in accordance with the invention, firstcontacts that surface. If flat-rolled steel, as supplied for asingle-surface coating embodiment includes coiling solution, sufficientflame impingement can be used on that remaining surface for burn-off ofthat solution, as indicated by the single burner, shown in interruptedlines, in FIG. 2.

To enhance polymeric coating adhesion, facilitate fabrication, andprovide durability for market-usage products, the invention teachesutilization of flat-rolled steel surfaces substantially free of millscale. A metallic corrosion-protective coating is selected, whichrequires removal of mill scale for application and, as applied, preventsiron-oxide formation on the substrate surface. That metallic coating isalso selected to be capable of responding to the described surfacepre-treatment for enhancing bonding of a selected polymeric coatingmaterial of the invention. Metallic corrosion protection can be carriedout by electrolytic plating, hot-dip molten metal coating, orconversion-coating of the flat-rolled steel substrate surface, forexample, by using a dichromate. That oxide-free metalliccorrosion-protected sub-surface, in combination with activation foradhesion of a combination of selected polymeric coating materials,produces engineered composite-coated work-product for increasingfabricating opportunities for, and durability of, market fabricatedproduct.

Referring to FIG. 1, subsequent to pre-treatment of a single-surface,multiple selected polymeric coating materials, as heated andpressurized, are extruded at station 26; as adherent molten film layersextending across strip width and, purposefully, extending so as toestablish polymeric overhang along each elongated lateral edge of thestrip. Utilizing that polymeric overhang enables achieving uniformpolymeric coating thickness across strip width, as described in moredetail in relation to later FIGS.

With solidification of the polymeric coating materials, polymericoverhang is removed, along each lateral edge, at station 28 of FIG. 1.Removal of polymeric overhang is carried-out prior to measuringpolymeric coating thickness at station 30. That thickness measurementenables signal feedback at station 32 for controlling polymeric coatingthickness on a continuing basis. Coating thickness correction, asutilized for achieving substantially uniform coating thickness, can bedirected to polymeric coating station 26 which can provide quantitativecontrol of extrusion; and/or can be directed to station 20 forline-speed control.

After edge trimming at station 28 and steps associated with measuringpolymeric coating thickness at station 30, the single-surfacepolymeric-coated strip is directed for finishing-processing of theinvention. Finishing processing is initiated at station 34 of FIG. 1, byheating the polymeric coating materials to a temperature exhibiting meltcharacteristics. That step, along with a selected brief interval ofin-line travel, in that heated condition prior to cooling, helps toaugment polymeric adhesion by filling and covering the topography of asurface, which can be finely-pitted due to mill-scale removal prior tometallic-protective coating. That re-melting during finish-processingcan add a mechanical adhesion factor, augmenting chemical bonding withthe substrate surface; and, that re-melting also augments the bondingbetween the selected polymeric coating layers of the invention.

The polymeric coating material is then rapidly cooled through glasstransition temperature at station 35 of FIG. 1 which contributessignificant advantages to the polymeric-coating. The thermoplasticpolymeric materials, selected as part of the invention, exhibit highstrength characteristics, however, they can also tend to exhibitcrystalline characteristics. Heating to a temperature range providingmelt characteristics for the polymeric materials, followed by rapidcooling through glass transition temperature, establishes amorphouscharacteristics throughout the polymeric coating thickness; so as tosubstantially eliminate ultra-fine micro-fracturing of the polymericcoating, which could otherwise occur during fabrication of thework-product.

A controlled quench bath, as shown in later FIGS, is utilized for rapidcooling; the strip is then directed for removal of quench liquid anddrying at station 36 of FIG. 1. The polymeric coated strip can then bedirected to station 37 for optionally selecting an in-line work-productidentification step or direct recoiling.

FIG. 2 presents a cross-sectional view, in a vertical planeperpendicular to the strip along the central axis of travel, ofpre-treatment. The number of open-flame impingement burner rows ofstation 39, extending across strip width, can be selected depending online speed and conditions at the strip surface. A single-surface ispre-treated at-a-time in order to augment polymeric adhesion. However,when pre-treating strip for solely single-surface polymeric coated,minimal opposite-surface burner exposure can be utilized, as needed, forremoving residual coiling lube solution from that surface. It should benoted that continuous-strip, protected as taught herein, substantiallyeliminates any future requirement to use lubricating solution forrecoiling purposes.

A selected number of in-line rows of electrodes, or preferably,corona-discharge units, as indicated in station 40 of FIG. 2, alsoextend across full-surface width for maintaining, and/or enhancing,surface activation. Corona discharge safely ionizes gases contiguous tothe strip substrate surface, and electrical energy level per square footof surface area is selected to avoid electric arcing. The gas ionizingmeans and their energy level are selected based on strip width and linespeed in the continuous-line operations of the invention.

Referring to the schematic cross-sectional view of FIG. 3, a pluralityof thermoplastic polymers, as selected, are combined and prepared toenable extrusion as multiple molten thin-film adherent layers. Thepolymeric coating materials include anhydride-modified polypropylene,and a combination of thermoplastic polymers which contribute coatingcharacteristics facilitating fabrication and enhancing performance ofmarket-usage products. A preferred embodiment combines, in addition toan anhydride-modified polypropylene film layer which first contacts thepre-treated surface, one or more layers which combine polypropylene withspecified percentage, by weight, of polybutylene; the latter for addingpolymeric strength and providing surface flexibility during fabricationof market-product.

Referring to a lower-located strip-entry portion of FIG. 3,continuous-strip 42 is introduced for polymer coating, free of heatingrequirements for the strip; which, in itself, facilitatescontinuous-line operations, by diminishing complications. A singlepre-treated surface is presented for polymeric deposition. At theupper-located polymer supply portion of the apparatus of FIG. 3,provisions are shown for supplying up to three pre-selectedthermoplastic polymeric materials. Solid pellets of a desired polymericcombination are supplied to respective hoppers 44, 45, and 46. Eachhopper leads to its respective individually-heated connector structure50, 51, and 52. Heaters, such as 53, are located along the length ofeach said tubular connector structure; and, an insulating housing, suchas 54, can surround each tubular connector structure for helping tomaintain melt temperature characteristics for each respective polymericmaterial. Pressurized movement of each polymeric material also tends tomaintain a temperature sustaining melt characteristics; pressurizing canbe achieved by driven internally-mounted augers (not shown) within eachtubular connector for its respective polymeric material.

Each heated and pressurized polymeric material moves through respectivetransfer means 55, 56 and 57 located within heated block 58. Each saidtransfer means initiates molding a rectangular cross-sectionconfiguration for its respective polymeric material; the thickness ofthat configuration is decreased as its cross-strip related widthincreases during continued movement toward strip coating. Each saidcross-sectional configuration polymeric material is quantitativelycontrolled and directed to a single die 60; in which molten extrusiontemperature is maintained by heated block 62.

Extrusion die 60 of FIG. 3 acts as a final-die presenting an outletconfiguration shaping the multiple polymeric materials into distinctthin-film adherent layers which provide substantially the intended totalpolymeric coating thickness, as pre-selected. Die 60 extends acrossstrip width; and, also, purposefully extends beyond each elongatedlateral edge of the strip for forming polymeric overhang which, aftersolidification, is trimmed from each lateral edge, helping to providefor uniform polymeric coating thickness across strip width. The distinctadherent polymeric layers are extruded substantially-simultaneously fortravel associated with a single pre-treated surface of strip 42.

Referring to FIG. 3A, which is an expanded cross-sectional view of adesignated portion of FIG. 3, deposition of selected moltenthermoplastic polymeric materials, which are extruded as adherentthin-film layers by die 60 and are directed into a coating nip definedbetween pressure roll 64 and temperature-modulating roll 66 for travelwith a single activated surface of strip 42. Pressure roll 64,preferably made of Teflon®-coated neoprene, exerts nominal pressure onthe extruded polymeric materials so as to implement contact for travelwith the strip on the periphery of temperature-modulated roll 66. Thelength of travel on the circumferential surface of roll 66 is selected,and, the peripheral surface temperature of roll 66 is controlled, fromits interior, so as to facilitate initial solidification of thecomposite polymeric coating materials on roll 66 for continued travelin-line on the pre-treated substrate surface.

The molten polymeric layers are solidified as heat moves into theambient temperature strip; however, solidification, during travel atline-speeds which can exceed six hundred feet per minute (fmp), takesplace predominantly due to movement of heat into thecontrolled-temperature peripheral surface of temperature-modulating roll66. That surface is held at about one fifty to about one seventy fivedegrees Fahrenheit (150° to 175°); which is significantly below meltfilm temperature used in continuous operations; the melt temperature forthe thermoplastic polymers can approach three hundred fifty degreesFahrenheit; however, film temperature, as extruded can exceed fivehundred fifty degrees Fahrenheit. The solidified polymeric materialstravel around contact roll 67, and coated strip 68 exits traveling inthe direction indicated in FIGS. 3 and 3 A.

In handling and combining the above-described thermoplastic polymers,the anhydride-modified polypropylene layer is extruded so as to firstcontact the pre-treated substrate surface. The level of anhydride inthat combination is prescribed for supply; and, is selected for initialadherence based on factors such as line speed, bonding with an activatedmetallic substrate surface, bonding with adherent polymeric layer, so asto enable solidification during travel in continuous-line operations, asdescribed.

In a specific embodiment of the first contacting layer, and ofsubsequent polymeric materials, polypropylene is selected for meltstrength, which contributes to enabling initial wet-travel of thepolymeric materials during a strip travel rate which is made practicalby utilization of in-line melted extrusion deposition as shown in FIG.3A. The anhydride-modified polypropylene layer first contacts theactivated surface, an intermediate “bulk” layer containing polypropyleneand about fifteen to twenty five percent, by weight, polybutylene-can beused; and, a combination of polypropylene, with about five to tenpercent, by weight, polybutylene, is selected for the outer surfacelayer, in a two or three layer embodiment. The polybutylene helps tosubstantially eliminate ultra-fine micro-fractures, referred to as“crazing”, within the polymers which causes a frosty appearance.Eliminating crazing enhances fabricating capabilities for market-usageproducts. Desired colorants can be added in thepolybutylene/polypropylene layers; also, lubricants can be added whichare activated during fabrication of market products.

Adherence to the single pre-treated surface for travel, and polymericsolidification facilitate edge removing trimming of polymeric overhangfrom each lateral edge of single-surface coated strip 68. Forminglateral edge overhang at each lateral edge, solidifying, and removingthat overhang provide an important solution to an encountered problem.It was found that extruding thin-film polymeric coating across theflat-rolled strip width, to its lateral edges, prevented achievinguniform coating thickness; that is, extruding thin-film polymericcoating materials extending to each lateral edge, of ambient temperaturecontinuous-strip, caused edge build-up. Extruding thin-film layers froma width-wise elongated narrow-opening die, resulted in a semi-sphericalshape where extrusion stops due to cohesive necking-in at such alocation. By extruding to each lateral edge, that spherical build-upincreased the thickness of the polymeric materials contiguous to eachlateral edge of the strip; which, in turn, prevented an intended uniformpolymeric thickness across full strip width. Also, that edge build-uphad other disadvantages, for example, in later re-coiling, and,potentially, during fabrication of market-usage product.

To eliminate that edge build-up problem and associated disadvantages,the die outlet configuration for the extrusion die is constructed toextend across full strip width and, in addition, to extend beyond eachlateral edge of the strip so as to provide a polymeric overhang at eachlateral edge. After in-line solidification, as described above, thatpolymeric overhang, which includes said thickened lateral-edge portion,is removed at edge trimming station 70 of FIG. 3. That enablescontinuing accurate measurements of polymeric thickness across fullstrip width as shown in later FIGS.; and, enables maintainingsubstantially-uniform coating thickness across full strip width duringcontinuous-line operations.

The apparatus of the embodiment of FIG. 4 is located to provide forcontinuous-line production of polymeric coating solely on a singlesurface of metallic substrate. Continuous-strip 71 is directed throughlooping tower 72 and into surface pre-treatment station 73 for selectivesurface pre-treatments, as described above in relation to FIG. 2. Travelof strip 74, with an activated surface, is directed toward thermoplasticpolymer supply apparatus 75 for polymeric coating materials, which areheated, pressurized, and shaped for extrusion, as described in relationto FIGS. 3 and 3A.

In FIG. 4, strip 74 travels into a coating nip defined by pressure roll76 and temperature modulating roll 77. Polymeric coating materials, assupplied and prepared in apparatus 75, are extruded as thin-filmadherent layers into that coating nip; and, solidified during travelaround temperature-modulating roll 77. The extruded polymeric coatingextends across full strip width; and, in addition, extends beyond eachlateral edge to form a polymeric overhang.

Solidification of the selected polymeric coating materials is initiatedat temperatures below about three hundred thirty five to about threehundred fifty degrees Fahrenheit. Travel of the polymeric layers on thecircumferential surface of temperature-modulating roll 77, which is heldat about one hundred fifty to about one hundred seventy degreesFahrenheit, facilitates solidification of the polymeric materials. Thesingle-surface coated steel substrate travels around roll 78 to trimstation 79, for removal of solidified polymeric overhang from eachlongitudinally-extended lateral edge of the strip.

The thickness of the single polymeric coated surface is measured acrossstrip width at thickness gauge 80 and thickness signals, as generated,are transmitted to thickness control unit 81 for in-line control andmaintenance of desired coating thickness. That thickness control can beexercised by selecting from the group consisting of controlling pressurewithin extrusion apparatus 75, controlling line speed, controlling dieopening, and a combination of those. Coating thickness at incrementallyspaced locations across strip width can be controlled by controlling theconfiguration of the die opening, along its width-wise opening, atincrementally selected locations correlated with incremental measurementlocations across strip width.

Edge-trimmed single-surface polymeric coated strip 82 of FIG. 4 travelsin-line toward finish-processing. Finish-processing is initiated atheating apparatus 83. High-frequency induction heating rapidly heats thefast-moving steel substrate which transfers heat to the polymericcoating. However, surface-penetrating infra-red radiation heating of thepolymeric materials can be combined in an effort to provide for uniformheating throughout the polymeric coating; which helps to avoid undueresidual heat existing in the steel strip.

Finish-processing heating is selected to provide melt temperaturecharacteristics for the selected polymeric materials; and provision ismade for in-line travel time of the coated polymers and strip in thatheated condition; that can help to achieve full contact of the polymericcoating with what may be a finely pitted topography of the metallicsubstrate surface; which can add a mechanical type of adhesion to thepolymeric chemical bonding with that surface.

An important part of finish-processing is rapidly cooling the heatedthermoplastic polymeric coating materials through glass transitiontemperature. That rapid cooling from melt temperature through glasstransition temperature substantially eliminates crystallinecharacteristics in the polymers; and, fixedly establishesdesired-amorphous characteristics throughout the polymeric coatingthickness. Application of quench bath 84 of FIG. 4 is selected to alsoremove residual heat from the flat-rolled steel strip so as to avoid anyreheating of the thermopolymers above glass transition temperature.

To augment rapid cooling, when needed, coolant from bath 84 can bepumped through re-circulating line 86 for laminar-flow of through-entrystructure 87. A separate heat exchange means for removing heat from there-circulating coolant can also be used as needed dependent on linespeed, polymeric thickness, and steel thickness gauge; that is, aclosed-loop refrigerant-type liquid in thermal heat exchange with therecirculating quench liquid which can be deionized water or tap water,helps to more readily maintain desired coolant temperature for rapidcooling through glass transition temperatures. Bath agitation, due tothe selected line speed, or use of quench bath baffles, can help toprevent formation of thermal barriers which could inhibit a desired rateof cooling for establishing the desired amorphous characteristicsthroughout the polymeric-coating materials. In FIG. 4, quench liquiddrag-out by the strip is returned by wiper rolls 88, the coated strip isdried at station 89; and, directed for selective recoiling at 90 oridentification for fabricating at station 91.

FIG. 5 is an enlarged cross-sectional view of engineeredcomposite-coated work product, with polymeric coating on a singlesurface, produced using the single-surface embodiment of FIG. 4. Steelsubstrate 92 includes metallic corrosion-preventing coating on eachsubstrate surface, respectively 93, 94. Polymeric coating 95 includesmultiple distinct polymeric layers on a single substrate surface.Metallic corrosion-prevention coating thickness and polymeric compositecoating thickness are selected so as to contribute to particularmarket-usage for single-surface polymeric-coated work-product for suchuse of polymeric coated flat-rolled steel in construction, astwo-by-fours, beams, columns, rafter supports, and other buildingstructure units, particularly for interior usage; along with other usesin transportation products.

The continuous-line operations of the invention also facilitatesdual-surface polymeric coating. In a dual-surface coating embodiment, asingle surface is pre-treated at-a-time; that single surface activationis promptly followed by polymeric coating, solidification, edge-trimmingand thickness gauging. And, after carrying-out those coating productionsteps separately for each surface, finishing processing of both surfacesis carried out simultaneously.

Referring to FIG. 6, strip 96 is directed through a looping pit intosingle-surface pre-treatment station 97. A single surface is pre-treatedby selective combination of flame-impingement and ionizing gascontiguous to that surface, for surface activation, as described inrelation to FIG. 2. Single-surface pre-treated strip 98 is directedin-line for initial polymeric coating of that single surface. Multiplepolymeric coating materials are supplied to, heated and pressurizedwithin apparatus 99, for adherent molten thin-film extrusion,as-described in relation to FIG. 3. Pressure roll 100 andtemperature-modulation roll 101 define a coating nip, for initiatingpolymeric coating multiple adherent thin-film layers on that singlepre-treated surface; as described in relation to FIG. 3A.

Solidification of those polymeric coating materials is achieved duringcircumferential travel on the peripheral surface oftemperature-modulating roll 101; that peripheral surface is cooled asnecessary from internally of roll 101. The solidified single-surfacecoated strip, travels as previously described, to trim station 102, forremoval of solidified polymeric overhang from eachlongitudinally-extending lateral edge of the strip; and then tothickness measurement.

That polymeric coated single-surface confronts thickness gauge 103 atwhich thickness measurements can be carried-out at incrementally-spacedlocations extending across strip-width for that said single-surface.Thickness measurement signals from gauge 103 are transmitted, asindicated, to feedback unit 104 for direction to selectedthickness-control means. Thickness control signals are preferablytransmitted, as shown in FIG. 6, to extrusion die structure 105 formaintaining quantitative control of desired polymeric coating thickness,on a continuing basis, across that single coated surface. Such controlcan extend to adjustments at incrementally-spaced locations along theelongated extrusion die which widthwise of the strip.

Edge-trimmed, single-surface coated strip 106 is directed in thecontinuous-line so as to present its non-polymeric coated surface foractivation of that remaining surface at pre-treatment station 107,surface activation is carried out as described in relation to FIG. 2.After pre-treatment activation of the single remaining surface, thestrip is guided, within the continuous-line as shown, for polymericcoating of that surface. A combination of polymeric coating materials,as supplied to and prepared for extrusion as adherent thin-film layersby apparatus 108; as previously described in relation to FIG. 3.Pressure roll 109 and temperature-modulation roll 110 form a coatingnip, initial deposition and solidification are carried out as describedin relation to the enlarged view of corresponding rolls in FIG. 3A.

Strip, with solidified polymeric coating on that remaining surface,travels around roll 111; and, is directed to edge trim station 112 forremoval of polymeric overhang along each longitudinally-extendinglateral edge. The strip is then guided in-line in relation to presentthat separately said recently-coated surface for polymeric thicknessmeasuring at gauge 115. Thickness measurements are directed to feedbackcontrol unit 116; signals are preferably directed to extrusion controlapparatus 117 for maintaining desired substantially-uniform coatingthickness across said remaining surface of strip 118, as previouslydescribed.

The dual-surface polymeric coated strip 118 travels in-line forfinish-processing which is carried-out simultaneously on each surface ofthe dual-surface polymeric-coated work-product. Finish-processingincludes heating polymeric coatings to achieve melt temperaturecharacteristics for the polymeric coating materials. Heating station 120can provide for selective use of high-frequency induction for quicklyheating the strip; and, penetrating infra-red radiation may be used forhelping to produce uniform melt characteristics throughout the combinedpolymeric coating materials. In-line travel time in that heatedcondition helps to complete contact with and covering the entiretopography of the metallic surface,.as previously described, beforeentry into quench bath 121.

The temperature for establishing melt characteristics, and time at thattemperature during a brief travel interval, before entry into the quenchbath, augments surface bonding and prepares for establishing amorphouscharacteristics, free of crystalline characteristics, by therapid-cooling in quench bath 121.

Rapidly cooling through glass-transition temperature in quench bath 121of FIG. 6 functions to fix desired amorphous characteristics in thepolymeric coating; and, to provide a smooth exterior surface whichfacilitates later fabrication. That rapid cooling can be augmented usinga laminar-flow injection for recirculating coolant at entrance 122 ofFIG. 6. Maintaining a desired cooling temperature for the quench bathcan be augmented using a pump-activated recirculating line; and, thatcooling can be supplemented by closed-loop refrigerant-type cooling ofthe quench liquid, as previously described.

The line speeds available can also help to provide sufficient turbulencewithin the quench tank so as to help prevent forming of thermal barrierswhich also help to achieve rapid cooling uniformly on both coated stripsurfaces. Wringer-rolls 123 return strip drag-out of quench bath liquid;and, blower apparatus 124 dries the coated strip which is directed torecoiling station 125 or to station 126 for identifying for fabrication.

The above-described continuous-line embodiments which prepare a singlesurface at-a-time for polymeric coating, contribute to productionefficiencies enabling line speeds which can extend from about sixhundred to about fifteen hundred feet per minute, for both singlesurface and dual-surface embodiments. In the dual-surface embodiment ofFIG. 6, finishing-processing by heating of polymeric-coatings on opposedsurfaces simultaneously; and, rapid cooling of polymeric materials onboth surfaces simultaneously through glass transition temperature,contribute additionally to uniformity of polymeric coatingcharacteristics on both surfaces.

A dual-surface polymeric material coated work-product embodiment isshown in the expanded cross-sectional view of FIG. 7. Continuous-stripsteel is represented at 126; metallic corrosion-protective coating isrepresented at 127 and 128; and, polymeric coating, comprising distinctlayers, is represented at 129 and 130, in the expanded cross-sectionalview of FIG. 7.

In fabricating market-usage products, for example for canningcomestibles, a metallic corrosion protective coating (127, 128 of FIG.7) is preferably selected from cathodic dichromate, electrolyticchrome/chrome oxide plating and electrolytic tinplating. Thecontinuous-strip steel (126 in FIG. 7) is selected for desired tensilestrength with base weight from about forty-five to about one hundredthirty five pounds per base box (“base box” is defined as area of 31,360square inches); those base weights represents a thickness range of aboutfive mils (0.005″) to about fifteen mils (0.015″); and, tensile strengthof about forty to fifty thousand pounds per square inch ofsingle-reduced plate (referred to as SR 4,5).

However, the glass-like polymeric surface properties, the surfacestrength and adhesion of polymeric materials of the present invention,have been found to enable use of higher-tensile strength,lighter-weight, double-reduced steel. That increased tensile strengthflat-rolled steel is produced by a double cold reduction, in which thesecond cold reduction is carried out free of an intermediate anneal.Double-reduction of flat-rolled steel provides a tensile strength ofeighty to ninety thousand pounds per square inch (referred to as DR8,9), and can be used with present teachings at thicknesses of aboutfour mils (0.004″) to about seven mils (0.007″) for can bodies,easy-open end-closures, and other can parts.

Can products, other than three-piece cans, which require significantfabrication, for example, one-piece can bodies where height exceedsdiameter, have been largely dependent on use of single-reducedelectrolytic tinplated steel. Use of a chrome oxide coating had beensubstantially limited to three-piece cans fabricated with weldedside-seams and to flat end closure structures, other than safety-edgeeasy-open end closures. One concern was abrasive-wearing of one-piececan body tooling, during fabrication, due to the abrasivecharacteristics of chrome oxide.

The present coating methods and products provide for one-piece can bodyfabricating capabilities which can include double-reduced can stock,with corrosion-protection using cathodic dichromate, electrolyticallyplated chrome/chrome oxide, or electrolytically plated tin. The smoothsurface, high-strength, adherent polymeric coating of thosecomposite-coated work products enable market-usage fabrication ofone-piece can bodies in a range of diameters, from about 22/16″ (202) toabout 37/16″ with side wall height from about 22/16″ (206) to about413/16″ (413); such as: Diameter-Height Use 202-314 for example for tunacans, 307-317 for example for soup cans, and 211-413 for twelve ouncetomato juice or carbonated beverage cans.

And, in addition, because of contributions of the polymeric coatingmethods and finish-processing of work-product, such-one-piece can bodiescan be draw-processed free of spraying with liquid sheet-metal drawlubricants; for example, the disclosed polymeric material surface layerenables incorporating a lubricating compound which is activated duringfabrication.

Chrome/chrome oxide corrosion-protection coating can be selected in arange of:

3 to 13 mg. per square foot chrome, and

0.7 to 2.5 mg. per square foot chrome oxide.

Electrolytic tinplating for use with the polymeric coatings of presentteachings, can be in the range of:

from 0.05 pound per base box, to

about 1.35 pounds per base box

on each surface; or, with differential coatings per surface, within suchrange.

Cathodic dichromate conversion coatings can be coated by immersion orcan be electrolytically applied, from about one hundred fifty (plus orminus 100) to about six hundred fifty (plus or minus one hundred)micrograms per square foot.

FIG. 8 schematically presents a perspective view of a portion of anelongated market-usage product 140, for representing types ofstructures, fabricated from flat-rolled steel, which are used inbuilding construction; such as: flat-rolled steel substrate beams,columns, two-by-fours, duct-work, or panel members used for fabricatingbuilding units for interior and exterior usage; such as: doors, door andwindow framing, interior or exterior decorative moldings, dormersheathing, roofing, and roof-ridge structures; and, for fabricatingtransportation-vehicle panels and structural units.

FIG. 9 is a detailed cross-sectional view representative of angledfabrication, such as a corner portion formed from a composite-coatedflat-rolled steel in fabricating end-usage product 140. Steel substrate142 can be selected as SR 4,5 within a thickness range of about five andone half to about fifteen and one half mils (0.0055″to 0.0155″). Ametallic corrosion-protective coat, to prevent iron oxide formation, canbe selected from any of the previously listed metallic coating; but,preferably, consists of hot-dip zinc spelter layers 143, 144respectively on each surface. The extruded polymeric coating 145, 146,respectively, on each surface, can comprise two or three of the distinctlayers of polymeric materials as previously described; and, withpolymeric coating thickness in the range of about one mil (0.001″) toabout two mils (0.002″) per surface, which helps to deaden soundtransmitting by, and resonance within, sheet-metal building units; thosepolymeric coatings also act as a thermal barrier to offset the effect ofchanges in temperature within a building, or offset the surface effectof a temperature-gradient between an interior and an exterior wall. Apolymeric coating of up to about four mils (0.004″) can be selected foruse on weather-exposed exterior building structure surfaces for doors,for framing for doors or windows, for molding, and the like; while athinner polymeric coating can be selected for an interior surface, orfor the interior of a building.

A hot-dip zinc spelter coating for building structures can be selectedin a range, from about 0.04 up to 1.25 ounces per square foot bothsurfaces; about two ounces per square foot, total zinc spelter bothcoated surfaces, can be used for heavy-duty outdoor structures. Adifferential zinc spelter coating can also be selected for each coatedsurface in the above ranges.

Continuous-strip width for polymeric coating deposition, in accordancewith present teachings, is preferred in a range of about thirty six toabout forty inches; the dimensional specifications for apparatus forsurface pre-treatment, polymeric coating, and edge trimming can bespecified based on the width of the strip.

Polymeric coating materials combinations can be ordered for preparationto specifications from: Basell Polyolefins USA Inc., 2801 CentrevilleRoad, Wilmington, DE 19808.

Dimensional specifications as set forth herein can be provided forordering surface burners from: Flynn Burner Corp., New Rochelle, NY10802; for:

Corona discharge electrodes, to selected specifications can be providedby ordering from: Enercon Industries Corp., Menomonee Falls, WI 53502;for:

Polymeric extrusion apparatus to specifications, can be ordered from:Black Clawson Converting Machines, LLC., Fulton, NY 13069, and

Infra-red gauges for measuring polymeric coating thickness and feedbackequipment can be ordered to specifications from: NDC Engineering,Irwindale, CA 91706.

While specific combinations of materials, dimensional values, methodsteps, apparatus and uses have been set forth for purposes of disclosingembodiments of the invention, it should be noted that in the light ofthose disclosures, others skilled in the art are in a position to usepresent teachings to devise combinations and use values differing fromthose specified for purposes of the above disclosure; but, whichcontinue to rely on principles of the invention as above disclosed.Therefore, for purposes of interpreting the appended claims referenceshall be made to the above disclosure, and the described functions ofthe invention, for evaluating the scope of patentability of subjectmatter as recited in the claims.

1-11. (canceled)
 12. Continuous-line apparatus for polymeric coating ofcontinuous-strip flat-rolled steel substrate, comprising: A) means forsupplying rigid flat-rolled steel continuous-strip, of predeterminedwidth between longitudinally-extending lateral edges thereof, presentinga pair of substantially-planar opposed metallic substrate surfaces forcontinuous-line polymeric coating operations, B) pre-treatment means foractivating a single substrate surface at-a-time for polymeric coating,by selecting from the group consisting of: i) solely a single surface ofsaid strip, and ii) said pair of opposed surfaces, which includes meansfor separate pre-treatment of each said surface for polymeric coating;and in which iii) said pre-treatment means for a single surfaceat-a-time, are selected from the group consisting of: a) means forproducing open-flame impingement of said substrate surface, b)corona-discharge means for ionizing gaseous atmosphere contiguous tosaid substrate surface, and c) a combination of (a) and (b); C) meanssupplying thermoplastic polymers capable of molding into distinctpolymeric coating materials for use in said continuous-line operations;D) means for heating and pressurizing each said distinct polymericcoating material to enable molten extrusion; E) means directingcontinuous-strip travel presenting a single activated substrate surfacefor polymeric coating free of heating requirements for said strip; F)means for simultaneously extruding said molten polymeric coatingmaterials, as adherent thin-film layers i) extending across fullpre-treated surface width of said strip, and ii) extending further toform a polymeric overhand extending beyond each lateral edge of saidpre-treated surface, by iii) selecting from the group consisting of a)association with solely a single pre-treated substrate surface, and b)association separately with each said surface, as separatelypre-treated. 13-17. (canceled)